1. Field of the Invention
The present invention relates to a scanning probe microscope suited for obtaining surface information of samples based on a broad scanning speed range from a low speed to a high speed, and a processing apparatus utilizing the scanning probe microscope.
2. Description of the Related Art
A scanning probe microscope (hereinafter referred to as "SPM") is an instrument used for measuring uneven shapes and the like on a surface of a sample on a level of atom size. In the SPM, its probe with a pointed tip is brought close to the sample for distances on the order of nanometers (nm), and physical interactions such as an atomic force between the probe and the sample is detected. A force microscope included in a group of the SPMs, which is typically represented by a scanning atomic force microscope (hereinafter referred to as "AFM"), is an instrument used for measuring the uneven shapes (concave and convex shapes) on the surface of the sample by using a beam with a very low spring constant called "a cantilever" and detecting a displacement of the cantilever caused by its flexural deformation. This flexural deformation is produced by an atomic force between the probe disposed at a tip of the cantilever and the sample.
A typical configuration of main mechanical members and a control system for a conventional AFM will be described with reference to FIG. 13. The AFM is a general type of a contact mode. When measuring the shapes of the surface in the sample, the AFM operates as described below:
A displacement generated in a cantilever 82 having a probe 81 at a tip thereof is measured by means of an optical displacement detector called an optical lever mechanism which includes a laser source 83 and a photodetector (a position detector) 84. The optical lever mechanism has been known generally and widely as a mechanism for detecting the displacement of the cantilever in the AFM. Further, a tripod 85 is equipped with three piezoelectric elements 88a and 88b (a Y axis piezoelectric element is not shown) in directions along three axes (X, Y and Z axes: They are perpendicular to one another) which support a sample table 87 for mounting a sample 86. The tripod 85 operates as a three-dimensional actuator for scanning the sample by the probe in the X and Y directions and controlling a distance between the probe and the sample (or between the cantilever and the sample ) in the Z axis direction.
For measuring for the surface shape of the sample 86, the cantilever 82 equipped with the probe 81 is brought into a specified place by an approaching/separating mechanism (not shown), where an atomic force can act between the sample 86 and the probe 81. At this time, the probe 81 is subjected to the atomic force from the surface of the sample 86 and the cantilever 82 is flexuously deformed, or bent. When the cantilever 82 is flexuously deformed, an operation of the tripod 85 in the direction along the Z axis is controlled by a control circuit 89 so as to cause a deviation signal .DELTA.s to be zero. The deviation signal .DELTA.s is defined as a difference between a displacement signal s1 and a set value s0 set in advance. The displacement signal s1, which can be detected by the optical lever mechanism, represents the displacement of the cantilever 82 (the displacement of the probe 81) caused by the flexural deformation thereof. In other words, the displacement of the probe 81 caused by the flexural deformation of the cantilever 82 is controlled so as to be always equal to the set value s0, whereby the probe 81 is maintained in a condition where it is pressed toward the sample 86 with a constant force. When the probe 81 scans the surface of the sample 86 by driving each piezoelectric element of the tripod 85 with an X-Y scanning circuit (not shown) while controlling a force for pressing the probe 81 on the sample with the constant force, a control signal s3 in relation to the Z axis direction changes in correspondence to the uneven shape of the surface of the sample. The change of the control signal s3 represents the information about the uneven shape on the surface of the sample.
A scanning tunnel microscope disclosed by Japanese Patent Application Laid-Open No. 1-206202 may be cited as a related art. A scanning tunnel microscope is generally an instrument which detects the uneven shape of a surface of a sample by measuring a distance between a probe and the sample while utilizing a tunnel current flowing between the probe and the sample, and by controlling the tunnel current so that it is kept constant while the surface of the sample is scanned with the probe. The scanning tunnel microscope described in the above-mentioned literature has a feature of obtaining surface shape information by adding a correcting signal .DELTA.Z.sub.2 to a basic signal .DELTA.Z.sub.1 originally used for obtaining the surface shape information.
The conventional AFM described above has a problem that an operation control in the direction along the Z axis of the tripod 85 cannot follow the uneven shape of the surface, in particular, when a speed for scanning the sample 86 is increased in order to perform a high speed measurement. If the operation control in the Z axis direction cannot follow the uneven shape, it is difficult to obtain accurate information as to the uneven shape. Moreover, in accordance with circumstances about the scanning speed and surface shapes, there are some possibilities that the measurements cannot be performed at all.
Though the AFM described above is the general type of contact mode, the similar problems are posed by AFMs of other modes such as a tapping mode, or the SPMs of other type. In the SPMs of other type, the configuration for obtaining the information about the surface of the sample is almost the same as that of the above-mentioned AFM, except for particular configurations as the instruments and signals used for the detection and control. The SPMs of other type are also configured to detect a mutual action between the probe and the sample, which vary dependently on the distance between them, and to obtain the information about the surface of the sample based on the control signals obtained by scanning the probe or the sample while controlling operations in the Z axis direction so as to keep the mutual action constant. Accordingly, these SPMs also cannot obtain the surface information when the scanning is performed at high speeds where the operation control in the Z axis direction cannot follow the uneven shape of the surface of the sample.
Further, the scanning tunnel microscope disclosed by the literature mentioned above is not equipped with a member such as a cantilever which is deformed dependently on a force, and has a configuration entirely different from that of the instrument for detecting a force such as the above atomic force. Furthermore, the signal .DELTA.Z.sub.2 to be added to the signal .DELTA.Z.sub.1 is used as a correction signal which serves for enabling to obtain the information on the surface of the sample at a high scanning speed. In cases where the operation control cannot follow the uneven shape of the surface and the original signal cannot be obtained in particular, the scanning tunnel microscope can correct a servo error by using the correction signal only when the servo error is included within a specific range. When the servo error exceeds the specific range, however, the scanning tunnel microscope cannot correct the servo error and causes the probe to be broken.